This invention relates to novel spiro-furanohydantoin derivatives useful in the treatment of certain chronic complications arising from diabetes mellitus, such as diabetic cataracts and neuropathy, to pharmaceutical compositions containing such compounds and to a method of using these compounds. Although many oral antidiabetic agents, such as the sulfonyl ureas, effectively lower blood sugar levels, the prevention or alleviation of the chronic complications of diabetes, such as diabetic cataracts, neuropathy, retinopathy and nephropathy has proved harder to achieve. According to U.S. Pat. No. 3,821,383, aldose reductase inhibitors such as 1,3-dioxo-1H-benz[d,e]-isoquinoline-2(3H)-acetic acid and its derivatives are useful in this regard. Spiro-thienohydantoin derivatives are also aldose reductase inhibitors according to U.S. application Ser. No. 870,542. Such compounds inhibit the enzymatic reduction of aldoses, such as glucose and galactose, to the corresponding polyols, such as sorbitol and galactitol, thus preventing or reducing the harmful and unwanted accumulations of polyols in the lens and retina of the diabetically cataractous eye, the diabetically neuropathic peripheral nerve and the diabetically nephropathic kidney.